Processes for forming an aldehyde by the hydroformylation of an olefinically unsaturated organic compound in the presence of a rhodium phosphorus complex catalyst and free phosphorus ligand are well known in the art, as seen, e.g., by U.S. Pat. Nos. 3,527,809; 4,148,830; and 4,247,486. The most commonly recommended phosphorus ligands are monophosphines and monophosphite compounds, especially triphenylphosphine.
For instance, U.S. Pat. No. 3,527,809, the entire disclosure of which is incorporated herein by reference thereto, discloses a hydroformylation process where olefinically unsaturated organic compounds are hydroformylated with carbon monooxide and hydrogen in the presence of a rhodium-phosphorus complex catalyst and free phosphorus ligand to produce aldehydes in high yields at low temperatures and pressures, where the normal to iso- (or branch chain) aldehyde isomer ratio of product aldehydes is high.
It is also known that, under hydroformylation conditions, some of the product aldehydes may condense to form high boiling aldehyde condensation by-products such as aldehyde dimers or trimers. Commonly-assigned U.S. Pat. No. 4,148,830, the entire disclosure of which is incorporated herein by reference thereto, discloses the use of these high boiling liquid aldehyde consensation by-products as a reaction solvent for the catalyst.
In addition, commonly-assigned U.S. Pat. No. 4,247,486, the entire disclosure of which is incorporated herein by reference thereto, discloses a liquid phase hydroformylation reaction using a rhodium-phosphorus complex catalyst, wherein the aldehyde reaction products and some of their higher boiling condensation products are removed in vapor form from the catalyst containing liquid body (or solution) at the reaction temperature and pressure. The aldehyde reaction products and the condensation products are condensed out of the off gas from the reaction vessel in a product recovery zone and the unreacted starting materials (e.g., carbon monooxide, hydrogen and/or alpha-olefin) in the vapor phase from the product recovery zone are recycled to the reaction zone. Furthermore, by recycling gas from the product recovery zone coupled with make-up starting materials to the reaction zone in sufficient amounts, it is possible, using a C.sub.2 to C.sub.5 olefin as the alpha-olefin starting material, to achieve a mass balance in the liquid body in the reactor and thereby remove from the reaction zone at a rate at least as great as their rate of formation essentially all the higher boiling condensation products resulting from self condensation of the aldehyde product.
It is also known in the prior art that even in the absence of intrinsic poisons there may be deactivation of rhodium-phosphorus hydroformylation catalysts under hydroformylation conditions. Commonly-assigned U.S. Pat. No. 4,277,627, the entire disclosure of which is incorporated herein by reference thereto, indicates that the deactivation of rhodium hydroformylation catalysts under hydroformylation conditions in the substantial absence of extrinsic poisons is due to the combination of the effects of temperature, phosphine ligand: rhodium mole ratio, and the partial pressures of hydrogen and carbon monoxide and is termed an intrinsic deactivation. It is further disclosed therein that this intrinsic deactivation can be reduced or substantially prevented by establishing and controlling and correlating the hydroformylation reaction conditions to a low temperature, low carbon monoxide partial pressure and high free triarylphosphine ligand: catalytically active rhodium mole ratio.
Thus, despite the obvious advantages of the above inventions, the discovery that the use of rhodium catalysts which may prove to be more robust than conventional rhodium-based catalysts in that they may be able to better withstand more severe reaction conditions and/or improve the economics of the hydroformylation process is of no small importance to the state of the art.